Understanding protein import in diverse non-green plastids.

The spectacular diversity of plastids in non-green organs such as flowers, fruits, roots, tubers, and senescing leaves represents a Universe of metabolic processes in higher plants that remain to be completely characterized. The endosymbiosis of the plastid and the subsequent export of the ancestral cyanobacterial genome to the nuclear genome, and adaptation of the plants to all types of environments has resulted in the emergence of diverse and a highly orchestrated metabolism across the plant kingdom that is entirely reliant on a complex protein import and translocation system. The TOC and TIC translocons, critical for importing nuclear-encoded proteins into the plastid stroma, remain poorly resolved, especially in the case of TIC. From the stroma, three core pathways (cpTat, cpSec, and cpSRP) may localize imported proteins to the thylakoid. Non-canonical routes only utilizing TOC also exist for the insertion of many inner and outer membrane proteins, or in the case of some modified proteins, a vesicular import route. Understanding this complex protein import system is further compounded by the highly heterogeneous nature of transit peptides, and the varying transit peptide specificity of plastids depending on species and the developmental and trophic stage of the plant organs. Computational tools provide an increasingly sophisticated means of predicting protein import into highly diverse non-green plastids across higher plants, which need to be validated using proteomics and metabolic approaches. The myriad plastid functions enable higher plants to interact and respond to all kinds of environments. Unraveling the diversity of non-green plastid functions across the higher plants has the potential to provide knowledge that will help in developing climate resilient crops.

First Report of the Hop Cyst Nematode, Heterodera humuli, in Two Counties of the Yakima Valley Region, WA, USA.

Cyst nematodes are ranked as the second most damaging plant-parasitic nematode genus of crops worldwide (Jones et al. 2013). The hop cyst nematode, Heterodera humuli, has been reported to cause up to 38% reduction in dry hops per bine (Hay and Pethybridge 2003). America is the top hop producing country worldwide, with 75% of production occurring in Washington state, with the majority of this production occurring in the Yakima Valley region (USDA, 2019). In late 2019, 30 soil samples from 15 different fields were collected from the hop cvs. HBC 394, HBC 369, and YCR 14. Nematodes were extracted using an adapted centrifugal floatation method (Jenkins 1964) from 100 cc subsamples of soil. Twenty of these samples contained at least one cyst and 23 contained at least one juvenile. Body length of juveniles (n = 5) averaged + standard deviation 377.62 ± 4.76 µm which is consistent with H. humuli juvenile body measurements (Sen 1968). Three samples from Yakima County and two from Benton County were identified to the species level using sequences from the internal transcribed spacer (ITS) region of the 5.8S gene. The sequences (GenBank accession numbers MT840678 to MT840682) were amplified using forward primer 5.8S-F (5'-GTGATTCCATTCACCAHCTACCTG-3'), and reverse primer 5.8S-R (5'-TTCGCACTAATTATCGCAGTTGG-3'). Sequence comparison with available ITS (5.8S) sequences in GenBank using BLAST showed 99.85% identity to H. humuli for all five samples. Because COI sequences of H. humuli are not available, to provide an additional marker for species identification, we amplified the COI sequences by using (forward primer Hete-COI-F (5'-TTTGGDCAYCCHGARGTTTATGTT-3'), and reverse primer Hete-COI-R (5'-AYWGTAAAAAGGRRAATAAAACC-3') for these samples. Four COI sequences (GenBank accession numbers MT840683 to MT840686) were obtained. These COI sequences will be used to identify future H. humuli samples. To confirm pathogenicity, eight 1-gal pots were filled with a 90:10 play sand to potting soil mixture and one hop rhizome cv. 'Centennial' was planted in pots and maintained in a greenhouse. After above ground plant growth was observed, half the pots were inoculated with hand-picked H. humuli cysts from Yakima soil samples at a density of 10 cysts/100 cc of soil. The life cycle of H. humuli in potted experiments is 40 days (McNamara and Mende 1995). Forty-five days after inoculation, plant measurements were recorded and nematodes extracted from five 100 cc soil samples per pot as described above. Soil samples revealed that H. humuli populations had an average Reproductive Factor (RF = final nematode population/initial nematode population) of 2.08. Five cysts were crushed to determine eggs/cyst, which yielded an average of 101 eggs/cyst. Young infected hops lacked vigor, with all replicates stunted both in bine height and leaf length compared to healthy controls. Bine heights were reduced by an average of 40.4% in pots inoculated with H. humuli compared to control plants (P = 0.0016). Distribution of hop cyst within the United States is limited to the top four states for hop production: Washington, Oregon, Idaho and Michigan (Cobb 1962; Sen and Jensen 1967; Hafez et al. 2010, Warner and Bird, 2015). In 1962, Cobb reported H. humuli in Pierce County, Washington, but it had not been reported in Benton County and Yakima County until now. This is a significant finding that has the potential to impact the Washington state hop industry, valued at $475.7 million in 2019 (USDA, 2019). Due to the lack of known effective nematode control measures, the discovery of H. humuli in the major hop-growing region of Washington warrants concern.

Plastid transit peptides-where do they come from and where do they all belong? Multi-genome and pan-genomic assessment of chloroplast transit peptide evolution.

Subcellular relocalization of proteins determines an organism's metabolic repertoire and thereby its survival in unique evolutionary niches. In plants, the plastid and its various morphotypes import a large and varied number of nuclear-encoded proteins to orchestrate vital biochemical reactions in a spatiotemporal context. Recent comparative genomics analysis and high-throughput shotgun proteomics data indicate that there are a large number of plastid-targeted proteins that are either semi-conserved or non-conserved across different lineages. This implies that homologs are differentially targeted across different species, which is feasible only if proteins have gained or lost plastid targeting peptides during evolution. In this study, a broad, multi-genome analysis of 15 phylogenetically diverse genera and in-depth analyses of pangenomes from Arabidopsis and Brachypodium were performed to address the question of how proteins acquire or lose plastid targeting peptides. The analysis revealed that random insertions or deletions were the dominant mechanism by which novel transit peptides are gained by proteins. While gene duplication was not a strict requirement for the acquisition of novel subcellular targeting, 40% of novel plastid-targeted genes were found to be most closely related to a sequence within the same genome, and of these, 30.5% resulted from alternative transcription or translation initiation sites. Interestingly, analysis of the distribution of amino acids in the transit peptides of known and predicted chloroplast-targeted proteins revealed monocot and eudicot-specific preferences in residue distribution.

Genome-Scale Characterization of Predicted Plastid-Targeted Proteomes in Higher Plants.

Plastids are morphologically and functionally diverse organelles that are dependent on nuclear-encoded, plastid-targeted proteins for all biochemical and regulatory functions. However, how plastid proteomes vary temporally, spatially, and taxonomically has been historically difficult to analyze at a genome-wide scale using experimental methods. A bioinformatics workflow was developed and evaluated using a combination of fast and user-friendly subcellular prediction programs to maximize performance and accuracy for chloroplast transit peptides and demonstrate this technique on the predicted proteomes of 15 sequenced plant genomes. Gene family grouping was then performed in parallel using modified approaches of reciprocal best BLAST hits (RBH) and UCLUST. A total of 628 protein families were found to have conserved plastid targeting across angiosperm species using RBH, and 828 using UCLUST. However, thousands of clusters were also detected where only one species had predicted plastid targeting, most notably in Panicum virgatum which had 1,458 proteins with species-unique targeting. An average of 45% overlap was found in plastid-targeted protein-coding gene families compared with Arabidopsis, but an additional 20% of proteins matched against the full Arabidopsis proteome, indicating a unique evolution of plastid targeting. Neofunctionalization through subcellular relocalization is known to impart novel biological functions but has not been described before on a genome-wide scale for the plastid proteome. Further work to correlate these predicted novel plastid-targeted proteins to transcript abundance and high-throughput proteomics will uncover unique aspects of plastid biology and shed light on how the plastid proteome has evolved to influence plastid morphology and biochemistry.

Neuromuscular and perceptual responses during repeated cycling sprints-usefulness of a "hypoxic to normoxic" recovery approach.

PURPOSE: We investigated the consequence of varying hypoxia severity during an initial set of repeated cycling sprints on performance, neuromuscular fatigability, and exercise-related sensations during a subsequent set of repeated sprints in normoxia. METHODS: Nine active males performed ten 4-s sprints (recovery = 30 s) at sea level (SL; FiO2 ~ 0.21), moderate (MH; FiO2 ~ 0.17) or severe normobaric hypoxia (SH; FiO2 ~ 0.13). This was followed, after 8 min of passive recovery, by five 4-s sprints (recovery = 30 s) in normoxia. RESULTS: Mean power decrement during Sprint 10 was exacerbated in SH compared to SL and MH (- 34 ± 12%, - 22 ± 13%, - 25 ± 14%, respectively, p < 0.05). Sprint performance during Sprint 11 recovered to that of Sprint 1 in all conditions (p = 0.267). All exercise-related sensations at Sprint 11 recovered significantly compared to Sprint 1, with no difference for Set 2 (p > 0.05). Ratings of overall perceived discomfort, difficulty breathing, and limb discomfort were exacerbated during Set 1 in SH versus SL (p < 0.05). Compared to SL, the averaged MPO value for Set 2 was 5.5 ± 3.0% (p = 0.003) lower in SH. Maximal voluntary force and twitch torque decreased similarly in all conditions immediately after Set 1 (p < 0.05), without further alterations after Set 2. Peripheral and cortical voluntary activation values did not change (p > 0.05). CONCLUSION: Exercise-related sensations, rather than neuromuscular function integrity, may play a pivotal role in influencing performance of repeated sprints and its recovery.

Exercise-related sensations contribute to decrease power during repeated cycle sprints with limited influence on neural drive.

PURPOSES: We manipulated the inspired oxygen fraction (FiO2) to examine the effects of physiological perturbations on exercise-related sensations and the neural drive of the quadriceps during repeated, brief, maximal cycle sprints. METHODS: Nine active males completed a repeated sprint cycle protocol (10 × 4-s maximal sprints with 30 s of passive recovery) in normoxia (NM; FiO2 0.21) and severe normobaric hypoxia (HY; FiO2 0.13). Peak power, quadriceps Root Mean Squared electromyography (RMS EMG), physiological (heart rate, arterial oxygen saturation, blood lactate concentration) and perceptual responses were recorded. RESULTS: The 10 sprints in HY were associated with lower arterial oxygen saturation values compared to NM [80.7 ± 0.9 vs. 95.6 ± 0.6%; P < 0.001; effect size (ES) = 0.98], higher blood lactate values (11.9 ± 0.4 vs. 9.9 ± 0.9 mmol L-1; P = 0.05; ES = 0.36), and greater exercise-related sensations (~36%; P < 0.001; ES > 0.47). Mean power for sprints 1-10 were lower (-13 ± 3%; P = 0.001; ES = 0.79), and sprint decrement was more pronounced in HY compared to NM (21.4 ± 3.7 vs. 13.2 ± 2.7%; P = 0.003). There was a 17% decrease in RMS EMG activity from the first to the last sprint (P < 0.001; ES = 0.65), independent of condition (P = 0.597; ES = 0.04). CONCLUSIONS: Despite severe hypoxia exacerbating both physiological and perceptual perturbations, the performance decrement observed during the repeated sprint protocol did not coincide with an accentuated decline in RMS EMG activity. These data suggest that higher-than-normal exercise-related sensations or perceptions coincide with fatigue during repeated sprinting, independent of changes in neural drive, when the task characteristics are known beforehand.

Comparative ultrastructure of fruit plastids in three genetically diverse genotypes of apple (Malus × domestica Borkh.) during development.

KEY MESSAGE: Comparative ultrastructural developmental time-course analysis has identified discrete stages at which the fruit plastids undergo structural and consequently functional transitions to facilitate subsequent development-guided understanding of the complex plastid biology. Plastids are the defining organelle for a plant cell and are critical for myriad metabolic functions. The role of leaf plastid, chloroplast, is extensively documented; however, fruit plastids-chromoplasts-are poorly understood, especially in the context of the diverse metabolic processes operating in these diverse plant organs. Recently, in a comparative study of the predicted plastid-targeted proteomes across seven plant species, we reported that each plant species is predicted to harbor a unique set of plastid-targeted proteins. However, the temporal and developmental context of these processes remains unknown. In this study, an ultrastructural analysis approach was used to characterize fruit plastids in the epidermal and collenchymal cell layers at 11 developmental timepoints in three genotypes of apple (Malus × domestica Borkh.): chlorophyll-predominant 'Granny Smith', carotenoid-predominant 'Golden Delicious', and anthocyanin-predominant 'Top Red Delicious'. Plastids transitioned from a proplastid-like plastid to a chromoplast-like plastid in epidermis cells, while in the collenchyma cells, they transitioned from a chloroplast-like plastid to a chloro-chromo-amyloplast plastid. Plastids in the collenchyma cells of the three genotypes demonstrated a diverse array of structures and features. This study enabled the identification of discrete developmental stages during which specific functions are most likely being performed by the plastids as indicated by accumulation of plastoglobuli, starch granules, and other sub-organeller structures. Information regarding the metabolically active developmental stages is expected to facilitate biologically relevant omics studies to unravel the complex biochemistry of plastids in perennial non-model systems.

High altitude, prolonged exercise, and the athlete biological passport.

The Athlete Biological Passport (ABP) detects blood doping in athletes through longitudinal monitoring of erythropoietic markers. Mathematical algorithms are used to define individual reference ranges for these markers for each athlete. It is unclear if altitude and exercise can affect the variables included in these calculations in a way that the changes might be mistaken for blood manipulation. The aim of this study was to investigate the influence of the simultaneous strenuous exercise and low to high altitude exposure on the calculation algorithms of the ABP. 14 sea level (SL) and 11 altitude native (ALT) highly trained athletes participated in a 14-day cycling stage race taking place at an average altitude of 2496 m above sea level (min. 1014 m, max. 4120 m), race distances ranged between 96 and 227 km per day. ABP blood measures were taken on days -1,3,6,10,14 (SL) and -1,9,15 (ALT) of the race. Four results from three samples of two different SL athletes exceeded the individual limits at the 99% specificity threshold and one value at 99.9%. In ALT, three results from three samples of three different athletes were beyond the individual limits at 99%, one at 99.9%. The variations could be explained by the expected physiological reaction to exercise and altitude. In summary, the abnormalities observed in the haematological ABP´s of well-trained athletes during extensive exercise at altitude are limited and in line with expected physiological changes.

Peripheral fatigue is not critically regulated during maximal, intermittent, dynamic leg extensions.

Central motor drive to active muscles is believed to be reduced during numerous exercise tasks to prevent excessive peripheral fatigue development. The purpose of the present study was to use hypoxia to exacerbate physiological perturbations during a novel, intermittent exercise task and to explore the time-course and interplay between central and peripheral neuromuscular adjustments. On separate days, 14 healthy men performed four sets of 6 × 5 maximal-intensity, isokinetic leg extensions (1 repetition lasting ∼7 s) at 300°/s (15 and 100 s of passive rest between repetitions and sets, respectively) under normoxia (NM, fraction of inspired O2 0.21), moderate (MH, 0.14), and severe normobaric hypoxia (SH, 0.10). Neuromuscular assessments of the knee extensors were conducted before and immediately after each set. There was an interaction between time and condition on the mean peak torque produced during each set (P < 0.05). RMS/M-wave activity of the rectus femoris decreased across the four sets of exercise, but there was no difference between conditions (8.3 ± 5.1% all conditions compounded, P > 0.05). Potentiated twitch torque decreased post set 1 in all conditions (all P < 0.05) with greater reductions following each set in SH compared with NM but not MH (end-exercise reductions 41.3 ± 3.0% vs. 28.0 ± 3.2%, P < 0.05 and 32.1 ± 3.3%, P > 0.05). In conclusion, severe hypoxia exacerbates both peripheral fatigue development and performance decrements during maximal, intermittent, dynamic leg extensions. In contrast to observations with other exercise modes, during exercise involving a single muscle group the attenuation of central motor drive does not appear to independently regulate the development of peripheral muscle fatigue.

Stage racing at altitude induces hemodilution despite an increase in hemoglobin mass.

Plasma volume (PV) can be modulated by altitude exposure (decrease) and periods of intense exercise (increase). Cycle racing at altitude combines both stimuli, although presently no data exist to document which is dominant. Hemoglobin mass (Hbmass), hemoglobin concentration ([Hb]), and percent reticulocytes (%Retics) of altitude (ALT; n = 9) and sea-level (SL; n = 9) residents were measured during a 14-day cycling race, held at 1,146-4120 m, as well as during a simulated tour near sea level (SIM; n = 12). Hbmass was assessed before and on days 9 and 14 of racing. Venous blood was collected on days 0, 3, 6, 10, and 14. PV was calculated from Hbmass and [Hb]. A repeated-measures ANOVA was used to assess the impact of racing at altitude over time, within and between groups. [Hb] decreased significantly in all groups over time (P < 0.0001) with decreases evident on the third day of racing. %Retics increased significantly in SL only (P < 0.0001), with SL values elevated at day 6 compared with prerace (P = 0.02), but were suppressed by the end of the race (P = 0.0002). Hbmass significantly increased in SL after 9 (P = 0.0001) and 14 (P = 0.008) days of racing and was lower at the end of the race than midrace (P = 0.018). PV increased in all groups (P < 0.0001). Multiday cycle racing at altitude induces hemodilution of a similar magnitude to that observed during SL racing and occurs in nonacclimatized SL residents, despite an altitude-induced increase in Hbmass. Osmotic regulatory mechanisms associated with intense exercise appear to supersede acute enhancement of oxygen delivery at altitude.

The role of sense of effort on self-selected cycling power output.

PURPOSE: We explored the effects of the sense of effort and accompanying perceptions of peripheral discomfort on self-selected cycle power output under two different inspired O2 fractions. METHODS: On separate days, eight trained males cycled for 5 min at a constant subjective effort (sense of effort of '3' on a modified Borg CR10 scale), immediately followed by five 4-s progressive submaximal (sense of effort of "4, 5, 6, 7, and 8"; 40 s between bouts) and two 4-s maximal (sense of effort of "10"; 3 min between bouts) bouts under normoxia (NM: fraction of inspired O2 [FiO2] 0.21) and hypoxia (HY: [FiO2] 0.13). Physiological (Heart Rate, arterial oxygen saturation (SpO2) and quadriceps Root Mean Square (RMS) electromyographical activity) and perceptual responses (overall peripheral discomfort, difficulty breathing and limb discomfort) were recorded. RESULTS: Power output and normalized quadriceps RMS activity were not different between conditions during any exercise bout (p > 0.05) and remained unchanged across time during the constant-effort cycling. SpO2 was lower, while heart rate and ratings of perceived difficulty breathing were higher under HY, compared to NM, at all time points (p < 0.05). During the constant-effort cycling, heart rate, overall perceived discomfort, difficulty breathing and limb discomfort increased with time (all p < 0.05). All variables (except SpO2) increased along with sense of effort during the brief progressive cycling bouts (all p < 0.05). During the two maximal cycling bouts, ratings of overall peripheral discomfort displayed an interaction between time and condition with ratings higher in the second bout under HY vs. NM conditions. CONCLUSION: During self-selected, constant-effort and brief progressive, sub-maximal, and maximal cycling bouts, mechanical work is regulated in parallel to the sense of effort, independently from peripheral sensations of discomfort.

Thermal, physiological and perceptual strain mediate alterations in match-play tennis under heat stress.

OBJECTIVES: This study compared the thermal, physiological and perceptual responses associated with match-play tennis in HOT (∼34°C wet-bulb-globe temperature (WBGT)) and COOL (∼19°C WBGT) conditions, along with the accompanying alterations in match characteristics. METHODS: 12 male tennis players undertook two matches for an effective playing time (ie, ball in play) of 20 min, corresponding to ∼119 and ∼102 min of play in HOT and COOL conditions, respectively. Rectal and skin temperatures, heart rate, subjective ratings of thermal comfort, thermal sensation and perceived exertion were recorded, along with match characteristics. RESULTS: End-match rectal temperature increased to a greater extent in the HOT (∼39.4°C) compared with the COOL (∼38.7°C) condition (p<0.05). Thigh skin temperature was higher throughout the HOT match (p<0.001). Heart rate, thermal comfort, thermal sensation and perceived exertion were also higher during the HOT match (p<0.001). Total playing time was longer in the HOT compared with the COOL match (p<0.05). Point duration (∼7.1 s) was similar between conditions, while the time between points was ∼10 s longer in the HOT relative to the COOL match (p<0.05). This led to a ∼3.4% lower effective playing percentage in the heat (p<0.05). Although several thermal, physiological and perceptual variables were individually correlated to the adjustments in time between points and effective playing percentage, thermal sensation was the only predictor variable associated with both adjustments (p<0.005). CONCLUSIONS: These adjustments in match-play tennis characteristics under severe heat stress appear to represent a behavioural strategy adopted to minimise or offset the sensation of environmental conditions being rated as difficult.

Heat stress does not exacerbate tennis-induced alterations in physical performance.

OBJECTIVES: To assess the time course of changes in physical performance in response to match-play tennis under heat stress. METHODS: Two matches consisting of 20 min of effective playing time (2×10 min segments) were played in COOL (∼102 min; ∼22°C and 70% relative humidity (RH)) and HOT (∼119 min; ∼36°C and 35% RH) environments. Repeated-sprint ability (3×15 m, 15 s rest), 15 m sprint time with a direction change (180°), vertical jump height (squat and countermovement jumps) and leg stiffness (multirebound jumps) were assessed in 12 competitive male players prematch, midmatch and postmatch, and 24 and 48 h after match completion. RESULTS: During the repeated-sprint ability test, initial (+2.3% and +3.1%) and cumulated sprint (+1.5% and +2.8%) times increased from prematch to midmatch and postmatch, respectively (p<0.001), while the sprint decrement score did not change. Match-play tennis induced a slowing (average of both conditions: +1.1% and +1.3% at midmatch and postmatch time points; p=0.05) of 15 m sprint time with direction change. Compared with prematch, leg stiffness (-6.4% and -6.5%; p<0.001) and squat jump height (-1.5% and -2.4%; p=0.05), but not countermovement jump height (-0.7% and -1.3%; p>0.05), decreased midmatch and postmatch, respectively, regardless of the condition. Complete recovery in all physical performance markers occurred within 24 h. CONCLUSIONS: In tennis, match-related fatigue is characterised by impaired repeated-sprint ability, explosive power and leg stiffness at midmatch and postmatch, with values restored to prematch baseline 24 h into recovery. In addition, physical performance responses (match and recovery kinetics) are identical when competing in cool and hot environments.

Coping with heat stress during match-play tennis: does an individualised hydration regimen enhance performance and recovery?

OBJECTIVES: To determine whether an individualised hydration regimen reduces thermal, physiological and perceptual strain during match-play tennis in the heat, and minimises alterations in neuromuscular function and physical performance postmatch and into recovery. METHODS: 10 men undertook two matches for an effective playing time (ball in play) of 20 min (∼113 min) in ∼37°C and ∼33% RH conditions. Participants consumed fluids ad libitum during the first match (HOT) and followed a hydration regimen (HYD) in the second match based on undertaking play euhydrated, standardising sodium intake and minimising body mass losses. RESULTS: HYD improved prematch urine specific gravity (1.013±0.006 vs 1.021±0.009 g/mL; p<0.05). Body mass losses (∼0.3%), fluid intake (∼2 L/h) and sweat rates (∼1.6 L/h) were similar between conditions. Core temperature was higher during the first 10 min of effective play in HOT (p<0.05), but increased similarly (∼39.3°C) on match completion. Heart rate was higher (∼11 bpm) throughout HOT (p<0.001). Thermal sensation was higher during the first 7.5 min of effective play in HOT (p<0.05). Postmatch knee extensor and plantar flexor strength losses, along with reductions in 15 m sprint time and repeated-sprint ability (p<0.05), were similar in both conditions, and were restored within 24 h. CONCLUSIONS: Both the hydration regimen and ad libitum fluid consumption allowed for minimal body mass losses (<1%). However, undertaking match-play in a euhydrated state attenuated thermal, physiological and perceptual strain. Maximal voluntary strength in the lower limbs and repeated-sprint ability deteriorated similarly in both conditions, but were restored within 24 h.

Voluntary muscle and motor cortical activation during progressive exercise and passively induced hyperthermia.

This study examined whether central fatigue was exacerbated by an increase in muscle contractile speed caused by passive hyperthermia (PaH) and whether exercise-induced hyperthermia (ExH) combined with related peripheral fatigue influenced this response. The ExH was induced by cycling at 60% of maximal oxygen uptake in 38°C conditions and the PaH by sitting in a 48°C climate chamber. Ten men performed brief (≈ 5 s) and sustained (30 s) maximal voluntary isometric contractions (MVCs) of the knee extensors at baseline (CON, ∼37.1°C) and during moderate (MOD, ≈ 38.5°C) and severe (SEV, ∼39.5°C) hyperthermia. Motor nerve and transcranial magnetic stimulation were used to assess voluntary muscle and cortical activation level, along with contractile properties. Brief MVC force decreased to a similar extent during SEV-ExH (-8%) and SEV-PaH (-6%; P < 0.05 versus CON). Sustained MVC force also decreased during MOD-ExH (-10%), SEV-ExH (-13%) and SEV-PaH (-7%; P < 0.01 versus CON). Motor nerve and cortical activation were reduced on reaching MOD (≈ 3%) and SEV (≈ 5%) ExH and PaH during the brief and sustained MVCs (P < 0.01 versus CON). Peak twitch force decreased on reaching SEV-ExH and SEV-PaH (P < 0.05 versus CON). Following transcranial magnetic stimulation, during the brief and sustained MVCs the peak muscle relaxation rate increased in ExH and PaH (P < 0.01 versus CON). The increase was greatest during the sustained contraction in SEV-PaH (P < 0.01), but this did not exacerbate central fatigue relative to ExH. These results indicate that during fatiguing cycling exercise in the heat, quadriceps peak relaxation rate increases. However, the centrally mediated rate of activation appears sufficient to overcome even the largest increase in muscle relaxation rate, seen during SEV-PaH.

An integrative test of agility, speed and skill in soccer: effects of exercise.

OBJECTIVES: The aim of this study was to evaluate the effect of 45 min of soccer-specific exercise in the reactive motor skills test (RMST); a novel test which measures sprint, passing and reactive agility (RAT) performance. DESIGN: A repeated-measures design was used to collect performance data. METHODS: Forty-two high-level amateur male soccer players (age 18.5±3.5 years) were recruited. Participants were familiarised with the RMST prior to initial testing. Participants undertook 10 repetitions of the RMST before and after 45 min of soccer-specific exercise using the Loughborough Intermittent Shuttle Test. Eighteen of these participants repeated the RMST for test re-test reliability determination. Paired t-tests and effect size statistics were used to determine the effect of 45 min of intermittent exercise on RMST performance. Reliability was assessed using the standard error of measurement. RESULTS: The exercise protocol resulted in moderate decreases of sprint (3.0±0.9%, mean±SD; 1.030±0.09 ES±90% Confidence Intervals; p<0.00001) and RAT performance (1.5±1.1%; 1.015±0.011; p<0.05), but improved passing task time (-2.7±1.2%; 0.973±0.012; p<0.001) and passing accuracy (3.6±3.3%; 1.036±0.33). Change in total test time was trivial. The test-retest coefficient of variation for the test was 2.4±0.8%. CONCLUSIONS: Soccer-specific exercise decreased sprint and reactive agility performance but improved technical skill performance on a novel, integrative and reliable test of soccer skill performance. Overall RMST performance time was largely unchanged.